Study On Preparation And Modification Of LiNi_0.5Mn_1.5O₄and LiNi_1/3Co_1/3Mn_1/3O₂Cathode Materials For Lithium Ion Battery

The preparation and modification of spinel high-voltage cathode materialLiNi_0.5Mn_1.5O₄and layered cathode material LiNi_1/3Co_1/3Mn_1/3O₂weresystematacially studied in this paper. The electrochemical properties ofLiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂and LiNi_1/3Co_1/3Mn_1/3O₂/Li₄Ti₅O₁₂full cells were alsodiscussed preliminarily.With NiCO₃·2Ni（OH）₂·4H₂O as Ni source, LiNi_0.5Mn_1.5O₄cathode materialsynthesized by ball-milling solid state method under the optimal process conditions（800℃,20h）, could reach a discharge capacity of105.6mAh·g^-1at the rate of1Cwith the capacity retention of89.7%after100cycles.The effect of low-temperature annealing treatment on the structure andelectrochemical performance of spinel LiNi_0.5Mn_1.5O₄cathode material was studiedby the optimized sol-gel method. The results showed that the content of Mn³⁺in theproduct was decreased and highly purity product was obtained after annealingtreatment. The annealed material with good electrochemical performance could reacha discharge capacity of125.0mAh·g^-1at the rate of1C with the capacity retention of97.6%after100cycles.The Cu²⁺doped LiNi_0.45Cu_0.05Mn_1.5O₄cathode material had been preparedsuccessfully. It was found that doping with Cu²⁺could reduce the electrodepolarization and ameliorate the cycle performance of the spinel at high rate and hightemperature. The LiNi_0.45Cu_0.05Mn_1.5O₄cathode material could reserve95.7%of theinitial discharge capacity (114.2mAh·g^-1) after150cycles at the discharge rate of20C, and could deliver127.3mAh·g^-1at high temperature （55℃） and5C with acapacity fading rate of2.0%after100cycles.Multiple ion doped LiNi0.475Al0.01Cr0.04Mn1.475O₃.95F0.05cathode material wasfirstly reported, which could achieve136.6,134.0,129.0,119.9,104.5and86.4mAh·g^-1at0.2C,1C,5C,10C,15C and20C, respectively. In addition, whencycled at55℃for100cycles, the capacity fading rates were only0.3%and4.4%at1C and10C, respectively. After multiple ion doping, the electrochemical reaction activity and cycle reversibility of the material had been improved, promoting theenhancement of its charge-discharge performance at high current.A cheap and nontoxic urea-based sol-gel method for the synthesis ofLiNi_0.5Mn_1.5O₄cathode material was proposed for the first time. The obtainedmaterial could achive132.1,123.3and113.0mAh·g^-1at1C,3C and5C,respectively. In addition, in the research of the electrochemical performance ofLiNi_0.5Mn_1.5O₄/Li₄Ti₅O₁₂full cell, the cell designed by some excess positive capacityshowed preferable cycle life and reversibility, which could achive98.7mAh·g^-1after200cycles at0.5C and the coulombic efficiencies were around99%.Layered LiNi_1/3Co_1/3Mn_1/3O₂cathode material was synthesized by hightermperature solid state method with LiOH·H₂O and Ni_1/3Co_1/3Mn_1/3（OH）₂as rawmaterials. The full cell (LiNi_1/3Co_1/3Mn_1/3O₂/Li₄Ti₅O₁₂) matched with Li₄Ti₅O₁₂anodematerial could reach the discharge capacity of147.3,139.2,119.6and86.0mAh·g^-1at0.2C,1C,5C and10C, respectively. Besides, it also could reserve83.7%after1000cycles at the rate of5C, revealing excellent charge-discharge performance andcycle life at high current.